A Quantitative Criterion for Defining Planets

A Quantitative Criterion for Defining Planets

Authors:

Margot et al

Abstract:

A simple metric can be used to determine whether a planet or exoplanet can clear its orbital zone during a characteristic time scale, such as the lifetime of the host star on the main sequence. This criterion requires only estimates of star mass, planet mass, and orbital period, making it possible to immediately classify 99% of all known exoplanets. All 8 planets and all classifiable exoplanets satisfy the criterion. This metric may be useful in generalizing and simplifying the definition of a planet.

Is There a Link Between Exoplanets & Circumstellar Debris Disks?

PURSUING THE PLANET–DEBRIS DISK CONNECTION: ANALYSIS OF UPPER LIMITS FROM THE ANGLO-AUSTRALIAN PLANET SEARCH

Authors:

Wittenmyer et al

Abstract:

Solid material in protoplanetary disks will suffer one of two fates after the epoch of planet formation; either being bound up into planetary bodies, or remaining in smaller planetesimals to be ground into dust. These end states are identified through detection of sub-stellar companions by periodic radial velocity (or transit) variations of the star, and excess emission at mid- and far-infrared wavelengths, respectively. Since the material that goes into producing the observable outcomes of planet formation is the same, we might expect these components to be related both to each other and their host star. Heretofore, our knowledge of planetary systems around other stars has been strongly limited by instrumental sensitivity. In this work, we combine observations at far-infrared wavelengths by IRAS, Spitzer, and Herschel with limits on planetary companions derived from non-detections in the 16 year Anglo-Australian Planet Search to clarify the architectures of these (potential) planetary systems and search for evidence of correlations between their constituent parts. We find no convincing evidence of such correlations, possibly owing to the dynamical history of the disk systems, or the greater distance of the planet-search targets. Our results place robust limits on the presence of Jupiter analogs which, in concert with the debris disk observations, provides insights on the small-body dynamics of these nearby systems.

A Survey of the Known and Potentially Upcoming in Exoplanetary Science

Galactic planetary science

Authors:

Tinetti et al

Abstract:

Planetary science beyond the boundaries of our Solar System is today in its infancy. Until a couple of decades ago, the detailed investigation of the planetary properties was restricted to objects orbiting inside the Kuiper Belt. Today, we cannot ignore that the number of known planets has increased by two orders of magnitude nor that these planets resemble anything but the objects present in our own Solar System. Whether this fact is the result of a selection bias induced by the kind of techniques used to discover new planets -mainly radial velocity and transit - or simply the proof that the Solar System is a rarity in the Milky Way, we do not know yet. What is clear, though, is that the Solar System has failed to be the paradigm not only in our Galaxy but even 'just' in the solar neighbourhood. This finding, although unsettling, forces us to reconsider our knowledge of planets under a different light and perhaps question a few of the theoretical pillars on which we base our current 'understanding'. The next decade will be critical to advance in what we should perhaps call Galactic planetary science. In this paper, we review highlights and pitfalls of our current knowledge of this topic and elaborate on how this knowledge might arguably evolve in the next decade.More critically, we identify what should be the mandatory scientific and technical steps to be taken in this fascinating journey of remote exploration of planets in our Galaxy.

Hot Jupiters WASP-48b and HAT-P-23b Emission Spectra Observed

WARM SPITZER AND PALOMAR NEAR-IR SECONDARY ECLIPSE PHOTOMETRY OF TWO HOT JUPITERS: WASP-48b AND HAT-P-23b

Authors:

O'Rourke et al

Abstract:

We report secondary eclipse photometry of two hot Jupiters, WASP-48b and HAT-P-23b, at 3.6 and 4.5 μm taken with the InfraRed Array Camera aboard the Spitzer Space Telescope during the warm Spitzer mission and in the H and KS bands with the Wide Field IR Camera at the Palomar 200 inch Hale Telescope. WASP-48b and HAT-P-23b are Jupiter-mass and twice Jupiter-mass objects orbiting an old, slightly evolved F star and an early G dwarf star, respectively. In the H, KS , 3.6 μm, and 4.5 μm bands, respectively, we measure secondary eclipse depths of 0.047% ± 0.016%, 0.109% ± 0.027%, 0.176% ± 0.013%, and 0.214% ± 0.020% for WASP-48b. In the KS , 3.6 μm, and 4.5 μm bands, respectively, we measure secondary eclipse depths of 0.234% ± 0.046%, 0.248% ± 0.019%, and 0.309% ± 0.026% for HAT-P-23b. For WASP-48b and HAT-P-23b, respectively, we measure delays of 2.6 ± 3.9 minutes and 4.0 ± 2.4 minutes relative to the predicted times of secondary eclipse for circular orbits, placing 2σ upper limits on |ecos ω| of 0.0053 and 0.0080, both of which are consistent with circular orbits. The dayside emission spectra of these planets are well-described by blackbodies with effective temperatures of 2158 ± 100 K (WASP-48b) and 2154 ± 90 K (HAT-P-23b), corresponding to moderate recirculation in the zero albedo case. Our measured eclipse depths are also consistent with one-dimensional radiative transfer models featuring varying degrees of recirculation and weak thermal inversions or no inversions at all. We discuss how the absence of strong temperature inversions on these planets may be related to the activity levels and metallicities of their host stars.

Some Kepler Systems May Parallel Saturn's Moons Overstable Scenario

OVERSTABLE LIBRATIONS CAN ACCOUNT FOR THE PAUCITY OF MEAN MOTION RESONANCES AMONG EXOPLANET PAIRS

Authors:

Goldreich et al

Abstract:

We assess the multi-planet systems discovered by the Kepler satellite in terms of current ideas about orbital migration and eccentricity damping due to planet-disk interactions. Our primary focus is on first order mean motion resonances, which we investigate analytically to lowest order in eccentricity. Only a few percent of planet pairs are in close proximity to a resonance. However, predicted migration rates (parameterized by $\tau _n=n/{|\dot{n}|}$) imply that during convergent migration most planets would have been captured into first order resonances. Eccentricity damping (parameterized by $\tau _e=e/{|\dot{e}|}$) offers a plausible resolution. Estimates suggest τ e /τ n ~ (h/a)2 ~ 10–2, where h/a is the ratio of disk thickness to radius. Together, eccentricity damping and orbital migration give rise to an equilibrium eccentricity, e eq ~ (τ e /τ n )1/2. Capture is permanent provided e eq lsim μ1/3, where μ denotes the planet to star mass ratio. But for e eq gsim μ1/3, capture is only temporary because librations around equilibrium are overstable and lead to passage through resonance on timescale τ e . Most Kepler planet pairs have e eq > μ1/3. Since τ n Gt τ e is the timescale for migration between neighboring resonances, only a modest percentage of pairs end up trapped in resonances after the disk disappears. Thus the paucity of resonances among Kepler pairs should not be taken as evidence for in situ planet formation or the disruptive effects of disk turbulence. Planet pairs close to a mean motion resonance typically exhibit period ratios 1%-2% larger than those for exact resonance. The direction of this shift undoubtedly reflects the same asymmetry that requires convergent migration for resonance capture. Permanent resonance capture at these separations from exact resonance would demand μ(τ n /τ e )1/2 gsim 0.01, a value that estimates of μ from transit data and (τ e /τ n )1/2 from theory are insufficient to match. Plausible alternatives involve eccentricity damping during or after disk dispersal. The overstability referred to above has applications beyond those considered in this investigation. It was discovered numerically by Meyer & Wisdom in their study of the tidal evolution of Saturn's satellites.